The present invention relates generally to a mating thread formation, and more particularly to a mating thread formation which is suitable for substantially locking threaded members together and making it necessary to develop a high degree of prevailing torque to unfasten the mating threads.
Conventional mating nuts and bolts have threads which are of a helical configuration and wherein the internal threads of the nut are substantially the same in configuration as the external threads of the bolt, with the possible exception that sometimes the internal threads of the nut are very slightly larger in diameter than the external threads of the bolt. There may further be certain variances depending upon the tolerances required in constructing such nut and bolt devices. These external threads would, however, have substantially the same number of threads per inch, identical angles formed between the flanks of the thread and they would have the same helix or lead angle. These comprise the most common type of nut and bolt devices.
When using a conventional nut and bolt device on something which has movement associated therewith, it is usually necessary to tighten the nut with respect to the bolt to such a degree that the bolt will stretch slightly and by such action will keep the threads in tight engagement to a degree. It has been found, however, that once such nut becomes loose, that constant or intermittent vibrations will tend to rotate the nut with respect to the bolt to a point in which the nut will be completely separated from the bolt. For this reason many devices have been developed to prevent such a nut from being separated from the bolt. Such devices can vary from the use of a pin extending through the bolt to what is commonly referred to as a lock nut device.
Lock nut devices operate on many different principles. One type of lock nut device uses thread distortion to create the requirement of a high prevailing torque in order to turn the nut with respect to the bolt. This thread distortion is usually accomplished by taking a standard nut and punching inwardly thereon at least at one point about the periphery thereof, to such a degree that the inner threads are permanently distorted. Consequently, when this nut is screwed onto a bolt, a higher degree of prevailing torque will be necessary for relative rotation than if the threads of the nut exactly conformed to the threads of the bolt. One of the problems with such a lock nut device is that this secondary operation of punching is an added expense, and a further disadvantage of this type of lock nut is that after several uses, the thread on the bolt will be forced to conform to the distorted thread form on the nut such that it will not provide the desired high prevailing torque after such multiple uses.
Another way to cause locking and thereby a high prevailing torque necessary to turn the nut with respect to the bolt is to spray a locking material on the threads of the nut or the bolt or both. This, too, is somewhat expensive and inconvenient; and, furthermore, must be done each time the nut is removed from the bolt or the high degree of prevailing torque which is desired is not achieved.
Another common lock nut which has received commercial success, is a nut having a standard thread thereon, but which has a nylon insert in one end thereof. Such nylon insert is not initially threaded. Such nylon-type lock nut is constructed by having a chamber on one end of the nut which is initially open. An annular nylon member is then inserted into this opening and that end of the lock nut is then clamped over the nylon insert. It can be easily appreciated that these extra steps and extra elements are quite an added expense to the construction of such locking device. A further disadvantage of such a device is that such lock nut can only be screwed onto a bolt from one preselected side of the nut to achieve the desired locking. Furthermore, multiple uses of such a locking device significantly diminish the effectiveness thereof, because the nylon washer is deformed during each use. After many uses the nylon-type lock nut will not cause the desired high prevailing torque necessary for turning the mating threads.
It can therefore be appreciated that there is indeed a need for a simple and inexpensive lock nut which can be used many times without losing its effectiveness.